Mulitple gated pixel per readout

ABSTRACT

A system for providing an improved image of daytime and nighttime scene for a viewer within a vehicle is provided herein. The system includes: a pixel array sensor having a fully masked gate-off capability at a single pixel level, wherein the pixel array sensor is provided with an inherent anti-blooming capability at the single pixel level; wherein each pixel is gated by a corresponding transfer gate transistor having high transfer gate efficiency. The system further includes a gating unit configured to control the transfer gate transistors with pulsed or continuous wave modulated active and passive light sources, to yield a synchronized sensing signal from the sensor, wherein a single pulse is sufficient to cover the entire field of view of the sensor and the entire depth of field of the illuminated scene; and a processing unit configured to receive the synchronized sensing signal and process it.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase Application of PCT InternationalApplication No. PCT/IL2013/050331, International Filing Date Apr. 17,2013, claiming priority of U.S. Provisional Patent Application No.61/625,756, filed Apr. 18, 2012, both of which are hereby incorporatedin their entirety.

BACKGROUND

1. Technical Field

The present invention relates to the field of imaging system, and, moreparticularly, to active and/or passive imaging by multiple gated lownoise pixel per readout frame method.

2. Discussion of Related Art

U.S. Pat. No. 7,733,464 B2, titled “vehicle mounted night vision imagingsystem and method” teaches a device and method for improving visibilityconditions in a motor vehicle during low-visibility environment(nighttime or nighttime with poor visibility conditions such as rain,snow etc.). The system described in the aforementioned patent is basedon gated imaging technology (i.e. the imaging sensor utilizes reflectedlight signal). In addition, the aforementioned system implements asensor that is based on image intensification technology usingphotocathode and/or micro-channel plate. This type of imageintensification technology has inherent drawbacks in vehicularenvironment; sensitivity lose due to high temperature (above 50 degCelsius), sensitivity lose due to solar irradiance, burn effect due to aconstant static image projection to the photocathode, temporal noise andblooming (saturation) in an inter-scene dynamic range above 50 dB. Thistype of image intensification technology is also defined as an exportcontrol item under the WASSENAAR arrangement or equivalent exportcontrol jurisdictions which cause difficulties in civilian applicationsuch as Advanced Driver Assistance Systems (ADAS). In addition, thesystem described in the aforementioned patent does not offer the driverany daytime imaging capabilities due to above drawbacks.

European Patent No. EP 1 118 208 B 1, titled “measuring distances with acamera”, teaches a device and method for measuring distances with acamera referred to as a “3D camera”. Several gated pixel designs aredescribed with a reset switch and at least a single gate switch or witha reset switch and at least a single modulator by a Field EffectTransistor (FET). These pixel designs have an integrator which iscomprised of a storage capacitor and an amplifier. These gated pixeldesigns described in '208 B1 patent has low performance in low lightlevel signal (such as in gated imaging vehicular applications) due toreset noise levels (also known as “KTC” noise) which are inherent in theintegrator mechanism presented with the amplifier feedback in the pixel.In addition, noise levels and signal accumulation in the pixelintegrator are not referred while gate off in the aforementioned patent.Anti-blooming ratio between pixel to the pixel apart is an importantfeature in an imaging sensor based on an array of gated pixels coupledand synchronized to a light source. In such a system configuration, agated pixel can be bloomed (i.e. saturated even up to three magnitudesmore than a nominal unsaturated signal) due to highly reflected objects(i.e. retro-reflector, mirror perpendicular to imaging sensor/lightsource etc.) in the viewed and/or measured scenery. Anti-blooming ratiobetween pixel to pixel apart are not described in the aforementionedpatent.

BRIEF SUMMARY

One aspect of the present invention provides a system for providing animproved image of daytime and nighttime scene for a viewer. The systemaccording to embodiments of the present invention may be operativelyassociated with any moving platform. In one non limiting example, themoving platform is a vehicle. It is understood however that anyrecitation of a vehicle herein may indicate use with any movingplatform. In one embodiment, the system is located within a vehicle. Thesystem may include: a pixel array sensor having a fully masked gate-offcapability at a single pixel level, wherein the pixel array sensor isprovided with an inherent anti-blooming capability at the single pixellevel; wherein each pixel is gated by a corresponding transfer gatetransistor having high transfer gate efficiency. The system furtherincludes a gating unit configured to control the transfer gatetransistors with pulsed or continuous modulated wave active light source(i.e. light source part of the gated system such as laser, LED,artificial light source etc.) and passive light sources (i.e. passive inthe sense that the light sources are not part of the gated system suchas LED's, artificial light sources etc. but are located in the gatedsystem Field Of View [FOV]), to yield a synchronized sensing signal fromthe sensor, wherein a single pulse by the active light source issufficient to cover the entire field of view of the sensor and theentire depth of field of the illuminated scene; and a processing unitconfigured to receive the synchronized sensing signal and process it, toyield an improved image of the scene. In some embodiments the pixelarray sensor may be located within the vehicle and so reflections fromthe scene are attenuated by a windshield of the vehicle.

Another aspect of the present invention provides a method for enhancingimaging system mounted on a vehicle suitable for different lightconditions. The method includes controlling the “ON” and “OFF” time ofat least a single pixel synchronized to a gated source of illuminationsaid source of illumination may be an active source (i.e. part of thesystem) or passive source (i.e. passive in the sense that the lightsource is not part of the gated system such as LED, artificial lightsource etc. but is located in the gated imaging system FOV). In thepresent technique when the pixel is in “ON” duration it will accumulatelight pulse propagating from the desired object and will ignore pulsesoriginating from clutter sources (such as background, highly reflectiveobjects, specific modulation etc.) when turned to “OFF” duration. Onceall the desired pulses of light are accumulated in the pixel FloatingDiffusion (FD) or other method of pixel storage, the signal is readoutto provide a single frame image. The disclosed technique provides manyadvantages over the known art few of them are:

A better Signal to Noise Ratio (SNR) image by accumulation of desiredlight signal (pulsed or modulated) and reducing background signalaccumulation.

Immunity to high inter-scene dynamic range of the magnitude of 40 dB.For a multiple gated pixel array, the anti-blooming ratio is above 1,000(60 dB), and desired around 10,000 (80 dB), between a saturated pixel tothe third pixel apart.

Ability to synchronize to pulsed or modulated light in the multiplegated pixel Instantaneous Field Of View (IFOV) originating from a pulsedor modulated light source. Ability to conduct a direct Time of Flight(TOF) imaging with a synchronized source of light reflected back to themultiple gated pixel IFOV.

Ability to gate at least a single pixel and/or to gate at least a singlepixel array.

These, additional, and/or other aspects and/or advantages of the presentinvention are: set forth in the detailed description which follows;possibly inferable from the detailed description; and/or learnable bypractice of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more readily understood from the detaileddescription of embodiments thereof made in conjunction with theaccompanying drawings of which:

FIG. 1 is a schematic circuit diagram depicting a “gate-able” pixelaccording to some embodiment of the present invention;

FIG. 2 and FIG. 3 are timing charts illustrating an aspect according tosome embodiments of the present invention;

FIGS. 4A-4C shows formulation and units used in a simulation of anexemplary implementation in accordance with some embodiments of thepresent invention; and

FIG. 5 shows graphs of a simulation of the exemplary implementationaccording to some embodiments of the present invention.

DETAILED DESCRIPTION

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangement of the components setforth in the following description or illustrated in the drawings. Theinvention is applicable to other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

FIG. 1 illustrates the “gate-able” pixel schematic that may be providedby Complementary Metal Oxide Semiconductor (CMOS) standard fabricationtechnology. Each pulse of light (i.e. each gate) is converted to aproportional electrical signal by the Photo-Diode (PD) that may be apinned PD. The generated electrical signal from the PD is transferred byan electric field to the Floating Diffusion (FD) which acts as anintegrator (i.e. capacitor) accumulating each converted pulse of light.Two controllable pixel signals generate the pixel gate; the transfergate transistor (TX1) and the anti-blooming transistor (TX2). Theanti-blooming transistor has three main objectives; the first being partof the single light pulse gating mechanism when coupled to TX1 (i.e. TX2is turned from ON to OFF or TX2 is turned from OFF to ON), the secondpreventing undesired parasitic signal generated in the PD not to beaccumulated in the PD during the time TX1 is OFF (i.e. PD Reset) and thethird to channel excessive electrical signal originated in the PD whenTX1 is ON, hence the role of anti-blooming. Anti-blooming TX2controllable signal acts as an optical shutter which ends the singleaccumulated light pulse. Transfer gate transistor (TX1) is turned ONonly in a desired time and only for a desired duration which is coupledto TX2. Once all pulses of light were accumulated in the FD, the signalis readout to provide a single frame image.

Multiple gated low noise pixel may have a standard electric signal chainafter the “gate-able” PD, TX1, TX2 and PD configuration. This standardelectric signal chain may consist of a Reset transistor (RST) with therole of charging the FD with electrical charge using the pixel voltage(VDD), may consist of a Source Follower (SF) transistor converting theaccumulated signal (i.e. electrons) to voltage and may consist of aSelect (SEL) transistor connected to the column and/or row for a pixelarray.

This schematic circuit diagram depicting a “gate-able” pixel has aminimal of five transistors (“5T”). This pixel configuration may operatein a “gate-able” timing sequence as described hereinafter by FIG. 2 andFIG. 3. In addition this pixel may also operate in a standard 5T pixeltiming sequence or operate in a standard 4T pixel timing sequence. Thisversatile operating configuration (i.e. gating sequence or standard 5Tor standard 4T) enables to operate the pixel different lightingconditions. For example, gating timing sequence during low light levelin active gated mode (with gated illumination), 4T timing sequenceduring low light level during nighttime (without illumination) and 5Ttiming sequence during high light level during daytime. This schematiccircuit diagram depicting a “gate-able” pixel may also have additionalcircuits for internal Correlated Double Sampling (CDS) and/or for HighDynamic Range (HDR). Adding such additional circuits reduces thephoto-sensing fill factor (i.e. sensitivity of the pixel).

FIG. 2 illustrates a flow chart of the multiple gated low noise pixelarray timing sequence for an active gated imaging where each lightsource (such as originating from a laser and/or LED and/or arc light orany other triggered light source of the active gated imaging system)reflected pulse is synchronized to each pixel gate event. The timingsequence is illustrated (not to scale) by steps, where each stepindicates a period of time and a signal ON is indicated in a black cell.All the steps will be clearer in a flow chart:

Step A1: A pixel Select transistor (SEL) is ON providing the specificrow array selection from of all the array rows and pixel anti-blooming(TX2) is ON (i.e. VSS voltage level which is lower than VDD) providingundesired parasitic signal generated in the PD not to be accumulated inthe PD.

Step A2: Pixel Reset transistor (RST) is ON providing the pixel FD to befully deployed with charge and pixel anti-blooming (TX2) is ON providingundesired parasitic signal generated in the PD not to be accumulated inthe PD.

Step A3: Pixel reset signal is sampled providing the pixel FD signallevel prior accumulation of at least a single desired exposure (i.e.gate). The pixel reset signal may be subtracted from the pixel signalsample in step A18 to eliminate the offset signal (hence CDS which isdone externally to the pixel in a gated configuration as illustrated inFIG. 1). Anti-blooming (TX2) is ON providing undesired parasitic signalgenerated in the PD not to be accumulated in the PD.

Step A4: Pulse of light (part of the active gated imaging) source isgenerated and anti-blooming (TX2) is ON providing undesired parasiticsignal generated in the PD not to be accumulated in the PD.

Step A5: Pulse of light source (part of the active gated imaging)propagates to a desired distance and reflected back to the pixel andanti-blooming (TX2) is turned OFF providing the beginning of signalgenerated in the PD to be transferred via transfer gate (TX1).

Step A6: Pixel transfer transistor (TX1) is turned ON to transfer theelectrical signal generated in the PD to the FD followed byanti-blooming (TX2) turned back ON ending the single gate transfer eventand providing undesired parasitic signal generated in the PD not to beaccumulated in the PD. TX1 ON period is equal or shorter than the lightpulse time to accumulate the desired pulse reflected signal and toreduce background signal accumulation.

Step A7: Pixel transfer transistor (TX1) is OFF with and anti-blooming(TX2) is ON providing undesired parasitic signal generated in the PD notto be accumulated in the PD.

Step A8: Similar to Step A4 but may have different timing as to Step A4.For example, Step 4 duration was 1 μsec (Full Width Half Maximum) whileStep A8 duration is 0.5 μsec or Step A4 duration was 1 μsec while StepA8 duration is 1.5 μsec etc.

Step A9: Similar to Step A5 but may have different timing as to Step A5providing a different accumulation starting distance in the pixel FOV.For example, Step A5 duration was 1 μsec (i.e. equal to a startingdistance of about 150 m for light propagation in free space) while StepA9 duration is 0.5 μsec (i.e. equal to a starting distance of about 75 mfor light propagation in free space).

Step A10: Similar to Step A6 but may have different timing as to Step A6to accumulate a light source pulse duration in Step A8 (equal or shorterthan the light pulse time). The time provides a different accumulationdepth of field distance in the pixel FOV. For example, Step A6 durationwas 1 μsec (i.e. equal to a depth of field of about 150 m for lightpropagation in free space) while Step A10 is 0.6 μsec (i.e. equal to adepth of field of about 90 m for light propagation in free space).

Step A11: Similar to Step A7 but may have different timing as to StepA7.

Step A12-Step A15: Similar to Step A4-Step A7 and to Step A8-Step A11but may have different timings as indicated above. The pixel gate (lightexposure and accumulation) may be conducted once, twice or #X gates(events) per pixel readout.

Step A16: After at least a single gate transfer event, anti-blooming(TX2) may be ON providing undesired parasitic signal generated in the PDnot to be accumulated in the PD.

Step A17-Step A18: Standard pixel readout is provided. Whileanti-blooming (TX2) is ON providing undesired parasitic signal generatedin the PD not to be accumulated in the PD and in the FD , pixel selecttransistor (SEL) is ON and the accumulated pixel signal is readout fromthe FD via the Source Follower (SF) transistor.

In active gated imaging with an array of multiple gated low noise pixelsper readout, the timing sequence of gate transistor (TX1) and theanti-blooming transistor (TX2) of Step A5 duration and Step A6 durationfor at least a single light pulse (i.e. single gate) may vary from pixelto pixel or from pixel array cluster to pixel array cluster. Thisenables each pixel or pixel array cluster to accumulate a differentdepth of field distance and/or starting distance in the pixel FOV.

According to some embodiment, gating unit is further configured tosimultaneously gate at least two pixel clusters with different gatingparameters by independently controlling the transfer gate transistors ofthe pixels at the at least two pixel clusters. In addition, thedifferent gating parameters may include synchronization parameters inregard with one or more light source, to match a different sceneryvolume for the different pixel clusters. The scenery volume is definedas a volume portion in the scene that is defined by borders such asdifferent depth of field distance and/or starting distance in the pixelFOV.

FIG. 3 illustrates a flow chart of the multiple gated low noise pixelarray timing sequence for a passive gated imaging where pixel gatetiming may be synchronized or unsynchronized to an external light source(originating from a laser and/or LED and/or arc light or any othertriggered light source not part of the gated imaging system but islocated in the gated imaging system FOV) for example a traffic signflickering light source. In contrast with active gated imaging timingdescribed above, passive gated imaging timing of each gate (i.e. pixelexposure to light which is a function of TX1 and TX2) may not besynchronized to the pulse light source. The multiple gates (i.e.exposures) with different timings provides the adequate light sourcesignal level as to the background signal in a single pixel readout .Thetiming sequence is illustrated (not to scale) by steps, where each stepindicates a period of time and a signal ON is indicated in a black cell.All the steps will be clearer in a flow chart:

Step B1: A pixel Select transistor (SEL) is ON providing the specificrow array selection from of all the array rows and pixel anti-blooming(TX2) is ON (i.e. VSS voltage level which is lower than VDD) providingundesired parasitic signal generated in the PD not to be accumulated inthe PD.

Step B2: Pixel Reset transistor (RST) is ON providing the pixel FD to befully deployed with charge and pixel anti-blooming (TX2) is ON providingundesired parasitic signal generated in the PD not to be accumulated inthe PD.

Step B3: Pixel reset signal is sampled providing the pixel FD signallevel prior accumulation of at least a single desired exposure (i.e.gate). The pixel reset signal may be subtracted from the pixel signalsample in step B18 to eliminate the offset signal (hence CDS which isdone externally to the pixel in a gated configuration as illustrated inFIG. 1). Anti-blooming (TX2) is ON providing undesired parasitic signalgenerated in the PD not to be accumulated in the PD.

Step B4: Pulse of light source (not part of the gated imaging but islocated in the gated imaging system FOV) is generated and anti-blooming(TX2) is ON providing undesired parasitic signal generated in the PD notto be accumulated in the PD.

Step B5: Pulse of light source (not part of the gated imaging but islocated in the gated imaging system FOV) propagates and transmitted tothe pixel and anti-blooming (TX2) is turned OFF providing the beginningof signal generated in the PD to be transferred via transfer gate (TX1).

Step B6: Pixel transfer transistor (TX1) is turned ON to transfer theelectrical signal generated in the PD to the FD followed byanti-blooming (TX2) turned back ON ending the single gate transfer eventand providing undesired parasitic signal generated in the PD not to beaccumulated in the PD. TX1 ON period should be equal or shorter than thelight pulse time to accumulate the desired pulse transmitted signal andto reduce background signal accumulation.

Step B7: Pixel transfer transistor (TX1) is OFF with and anti-blooming(TX2) is ON providing undesired parasitic signal generated in the PD notto be accumulated in the PD.

Step B8: Similar to Step B4 but may have different timing as to Step B4.For example, Step B4 duration was 1 μsec (Full Width Half Maximum) whileStep B8 duration is 0.5 μsec or Step B4 duration was 1 μsec while StepB8 duration is 1.5 μsec etc.

Step B9: Similar to Step B5 but may have different timing as to Step B5providing different accumulation timing in the pixel FOV. For example,Step 5 duration was 1 μsec while Step B9 duration is 0.5 μsec.

Step B10: Similar to Step B6 but may have different timing as to Step B6to accumulate a light source pulse duration in Step B8 (equal or shorterthan the light pulse time). The time provides accumulation of lightsource pulse different duration time in the pixel FOV. For example, StepB6 duration was 1 μsec while step B10 is 0.6 μsec.

Step B11: Similar to Step B7 but may have different timing as to Step7.

Step B12-Step B15: Similar to Step B4-Step B7 and to Step B8-Step B11but may have different timings as indicated above. The pixel gate (lightexposure and accumulation) may be conducted once, twice or #X gates(events) per pixel readout.

Step B16: After at least a single gate transfer event, anti-blooming(TX2) may be ON providing undesired parasitic signal generated in the PDnot to be accumulated in the PD.

Step B17-Step B18: Standard pixel readout is provided. Whileanti-blooming (TX2) is ON providing undesired parasitic signal generatedin the PD not to be accumulated in the PD, pixel select transistor (SEL)is ON and the accumulated pixel signal is readout from the FD via theSource Follower (SF) transistor.

FIG. 3 illustrates also a flow chart of the multiple gated low noisepixel array timing sequence for a passive gated imaging where pixel gatetiming may accumulate signal of an external light source (originatingfrom a laser and/or LED and/or arc light or any other continuous lightsource which are not part of the gated imaging system but is located inthe gated imaging system FOV) for example sun irradiance. The at leastsingle gate (i.e. exposure) may provide the adequate signal level in asingle pixel readout. The timing sequence is illustrated (not to scale)by steps, where each step indicates a period of time and a signal ON isindicated in a black cell.

One of the key characteristic in the multiple gated low noise pixel isthe opaqueness during gate OFF. Generated parasitic electrical signal inthe FD while the pixel gate is OFF (i.e. TX1 at OFF and TX2 at ON) maybe reduced by masking the FD (for example, by metal layers in the pixelstructure) and/or by using the pixel micro-lens to channel the lightaway from the FD. Opaqueness during gate OFF levels are required to beas low as possible where response to the signal collected in a FDdivided by the intensity of light at the integration time(gating/non-gating and readout time) shall be up to 0.01%. This value isrequired to cope with the backscatter intensity reflection in activeimaging explained below.

The governing parameter of an active imaging performance is themodulation contrast which we is defines as “Contrast” in Eq.(1), takinginto account the air light, which is in this context light from ambientlight sources that are scattered into the system's FOV and backscatter,which add to the target and background.

$\begin{matrix}\begin{matrix}{{Contrast} = \frac{I_{Target}^{Total} - I_{Background}^{Total}}{I_{Target}^{Total} + I_{Background}^{Total}}} \\{{= \frac{I_{Target} - I_{Background}}{I_{Target} + I_{Background} + {2\; I_{Air}} + {2\; I_{Backscatter}}}},}\end{matrix} & (1)\end{matrix}$whereI _(Target) ^(Total) =I _(Target) +I _(Air) +I _(Backscatter)I _(Total) ^(Background) =I _(Background) +I _(Air) +I_(Backscatter.)  (2)I_(Air) is the air-light contribution to the focal plane illumination.For night vision, there is very little or no air light and I_(Air)≈0.This result may be achieved using a narrow band pass filter (i.e.spectral filter). For harsh weather imaging conditions (e.g. dust orfog), we must take the air-light into account. The following presents aconvenient method for predicting the effects of atmospheric backscatteron image quality when an artificial source near the image sensor is usedto illuminate a distant scene. It is assumed that the separation betweenilluminator and imaging system is small compared to the range to thenearest illuminated particles in the FOV. Then, the radiance of theatmosphere within the FOV is calculated by summing the backscattercontributions of all illuminated particles on the path between thesensor and the scene. The result is

$\begin{matrix}{{I_{Backscatter} = {\int_{2\;\gamma\; R_{\min}}^{2\;\gamma\; R_{\max}}{\frac{{PG}\;\gamma^{2}e^{- X}}{2\; F_{\# l}^{2}\theta_{l}^{2}X^{2}}\ {\mathbb{d}X}}}},} & (3)\end{matrix}$where

I_(Backscatter)=Radiance of atmospheric backscatter [Power/Area]

R_(min)=Range from imaging system (and from illuminator) to the nearestilluminated particles in the FOV [Length]

R_(max)=Range from imaging system (and from illuminator) to the scenebeing imaged [Length]

P=Radiant intensity of illuminator [Power]

G=Backscatter gain of atmospheric particles relative to isotropicscattering [dimensionless]

γ=Atmospheric attenuation coefficient or “extinction coefficient”[Length⁻¹]

F_(#1)=F number of the illuminator optics [dimensionless]

θ₁=Illuminator beam divergence [Angular]

X=Integration variable

With a narrow wavelength illuminator and the line-of-sight path throughthe atmosphere is taken to be horizontal, the atmospheric attenuationcoefficient is considered constant.

FIG. 4 and FIG. 5 illustrate another key characteristic in the multiplegated low noise pixel is the transfer gate transistor (TX1) noise (i.e.transfer efficiency). FIG. 4 provides the formulations and units used inthe simulation while FIG. 5 shows the results of the simulation. Inactive gated imaging eye and skin safety standards may limit the lightsource (e.g. laser, LED etc.) optical peak power, optical average poweretc. Gate transistor (TX1) noise (i.e. transfer efficiency) may be acrucial parameter in such a case. Gate transistor (TX1) noise (i.e.transfer efficiency) is a result of physical procedures of theelectrical charge transfer uncertainty level. At least three differentmethods may be implemented in the pixel to provide a higher gatetransfer (TX1) efficiency:

-   -   Setting a high potential voltage between the PD to the FD        enabling an intense electrical field which electrical charge        carriers (i.e. at least a single electron) have higher        probability to be “pulled” to the FD.    -   Physical dimensions of the transfer gate, mainly on the TX1 PD        side. As larger the transfer gate (TX1) the gate transfer        efficiency to the FD is larger and vice versa.    -   Physical structure of the transfer gate, mainly on the TX1 PD        side. As “flawless” (i.e. without “holes”) the transfer gate        (TX1) the gate transfer efficiency to the FD is larger and vice        versa.

The following example shall illustrate the influence of pixel signal,pixel noise level (only due to gate transfer) and pixel SNR. An exampleof a calculation of signal and noise levels (FIG. 5, graph #1):

-   -   A single light pulse accumulated signal (i.e. single gate        transfer) in the FD as a function of target distance.    -   Noise level of a single light pulse accumulated signal (i.e.        single gate transfer) in the FD as a function of target distance        and noise transfer equivalent to one electron.    -   Noise level (only due to gate transfer) of a single light pulse        accumulated signal (i.e. single gate transfer) in the FD as a        function of target distance and noise transfer equivalent to ten        electrons.

An example of a calculation of pixel SNR (FIG. 5, graph #2):

-   -   SNR as a function of a single light pulse accumulated signal        (i.e. single gate transfer), noise transfer equivalent to a        single electron and target distance.    -   Etc. with one hundred light pulses (i.e. one hundred gate        transfers).    -   SNR as a function of a single light pulse accumulated signal        (i.e. single gate transfer), noise transfer equivalent to ten        electrons and target distance.    -   Etc. with one hundred light pulses (i.e. one hundred gate        transfers).

In active gated imaging the raise time and fall time of transfer gatetransistor (TX1), anti-blooming transistor (TX2) and source of lightpulse are related directly to the depth of field distance and startingdistance resolution/accuracy.

In passive gated imaging the raise time and fall time of transfer gatetransistor (TX1), anti-blooming transistor (TX2) and source of lightpulse (not part of the gated imaging system but is located in the gatedimaging system FOV) are related directly to the signal accumulation ofthe pulse modulation.

The multiple gated pixel may have a thick Epitaxial layer above 12 μmand/or high resistivity layer as starting material for pixel waferproviding a higher PD spectral response (i.e. directly related to pixelfill factor and quantum efficiency) in the Near Infra-Red to valuesabove 50%. As the Epitaxial layer is thicker the spectral response islarger but the Modulation Transfer Function (MTF) of the pixel is lower.For active gated imaging used mainly for night vision application theMTF reduction due to the thick Epitaxial layer and/or high resistivitylayer is second order to the spectral response due to large pixeldimensions, preferably larger than 5 μm by 5 μm. The large pixel isrequired to accumulate more reflected light signal (i.e. larger pixelarea) whereas the resolution during low light level (e.g. less than 0.1lux) is not required.

Preferably, the multiple gated pixel and the multiple gated sensor (i.e.array of pixels with a readout interface) is produced using CMOStechnology which complies with vehicular environment; high temperaturestorage and operation (above 50 deg Celsius), sensitivity is not damageddue to solar irradiance, no burn effect due to a constant static imageprojection to the gated pixel.

Preferably, a spectral filter is introduced in front of the multiplegated pixel and/or the multiple gated sensor (i.e. array of pixels witha readout interface) in active imaging (i.e. coupled to a light source)or passive imaging (i.e. passive in the sense that the light source isnot part of the gated system such as LED, artificial light source etc.but is located in the gated imaging system FOV) to reduce ambient lightaccumulation at daytime, nighttime and other ambient light conditions.The spectral filter can be implemented in the pixel array level as amosaic filter array (e.g. arranging spectral filters on a square grid ofphoto-sensors). The filter pattern can be; is 25% green, 25% red, 25%blue and 25% Near Infra-Red (NIR), hence is also called RGBN. The filterpattern can also be; is 50% clear (e.g. open to a wide spectralwavelengths), 25% red and 25% NIR, hence is also called CCRN. The filterpattern can also be; is 25% clear, 25% NIR in one specific wavelengthand 25% NIR in a different specific wavelength, hence is also calledCRN(1)N(2) (e.g. C: 450-850 nm, R: ˜650 nm, N(1): 780-800 nm and N(2):810-850 nm). The filter pattern can also be any other combination ofgreen, red, blue, clear and NIR.

Preferably, a polarization filter is introduced in front of the multiplegated pixel and/or the multiple gated sensor (i.e. array of pixels witha readout interface) in active (i.e. coupled to a polarized lightsource) or passive imaging (i.e. passive in the sense that the lightsource is not part of the gated system such as LED, artificial lightsource etc. but is located in the gated imaging system FOV) to reduceambient light accumulation at daytime, nighttime and other ambient lightconditions.

Ability to conduct a direct TOF imaging with a synchronized source oflight reflected back to the multiple gated pixel FOV may also beachieved be several methods such as performing Steps A1-A7 and ratherthan performing Step A8 perform several times a sequence of Steps A6-A7with a short delay of ΔT between each sequence. Each delay of ΔTaccumulates a different portion of the depth-of-field of ΔZ=ΔT*C/2,where C is the speed of light. For example a delay of ΔT=100 nsecbetween sequences of Step A6-A7 shall provide a depth-of-field of 15 mfor each sequence.

While the invention has been described with respect to a limited numberof embodiments, these should not be construed as limitations on thescope of the invention, but rather as exemplifications of some of thepreferred embodiments. Other possible variations, modifications, andapplications are also within the scope of the invention. Accordingly,the scope of the invention should not be limited by what has thus farbeen described, but by the appended claims and their legal equivalents.

The invention claimed is:
 1. A system for providing an improved image ofdaytime and nighttime scene, the system comprising: a pixel array sensorhaving a masked gate-off capability at a single pixel level, wherein thepixel array sensor is provided with an inherent anti-blooming capabilityat the single pixel level, wherein each pixel is gated by acorresponding transfer gate transistor having a high transfer gateefficiency; and a gating unit configured to control the transfer gatetransistors of the pixel array sensor so as to accumulate a sequence ofmultiple exposures per single readout of the pixel based on specifiedexposure parameters, wherein the pixel sensor array is furtherconfigured to operate in at least one mode other than gating.
 2. Thesystem according to claim 1, wherein the pixel array sensor is attachedto a moving platform.
 3. The system according to claim 1, wherein thegating unit is configured to operate with a synchronized pulsed lightsource.
 4. The system according to claim 1, wherein the gating unit isconfigured to operate with an unsynchronized light source.
 5. The systemaccording to claim 1, wherein the gating unit is further configured tosimultaneously gate at least two pixel clusters with different gatingparameters by independently controlling the transfer gate transistors ofthe pixels at the at least two pixel clusters.
 6. The system accordingto claim 5, wherein the different gating parameters comprisesynchronization parameters in regard with one or more light source, tomatch a different scenery volume for the different pixel clusters. 7.The system according to claim 5, wherein the different gating parametersare selected, so that an independent accumulation of the signal iscarried out for each of the different pixel clusters.
 8. The systemaccording to claim 1, wherein the inherent anti-blooming capability atthe single pixel level exhibits a ratio of at least 60 dB between asaturated pixel at the pixel array and a second adjacent pixel.
 9. Thesystem according to claim 1, wherein a low noise in the pixel isachieved by resetting its potential voltage during a period without alight source pulse or light source modulation thus reducing parasiticnoise in the photodiode.
 10. The system according to claim 1, whereinthe high transfer gate efficiency is achieved by setting a highpotential voltage between the pixel to the floating diffusion of thetransfer gate thus enabling an intense electrical field which electricalcharge carriers have higher probability to be extracted to the floatingdiffusion.
 11. The system according to claim 1, wherein the hightransfer gate efficiency is achieved by setting physical dimensions ofthe transfer gate, such that the transfer gate at the photodiode side issubstantially larger than a transfer gate at the floating diffusionside.
 12. The system according to claim 1, wherein the high transfergate efficiency is achieved by setting the transfer gate at thephotodiode side to be substantially without holes.
 13. The systemaccording to claim 1, wherein the pixel is configured to detect lightwithin a range covering from 400 nm to 1100 nm.
 14. The system accordingto claim 1, wherein the pixel is configured to detect light within arange covering from 700 nm to 2 μm.
 15. The system according to claim 1,wherein the pixel array sensor configured to operate in conjunction withcolor filters.
 16. The system according to claim 1, wherein the activelight source pulses or active light source modulation are NIR atapproximately 800 nm.
 17. The system according to claim 1, wherein thepixel array sensor is sufficiently sensitive to detect reflectionsarriving from a distance of between approximately 20 m and 200 m whereinthe reflection are attenuated prior to reaching the pixel array sensorat least two orders of magnitude.